The present invention relates to a driving machine, and more particularly to the driving machine having a cylinder fixing arrangement for improving the ease with which a cylinder can be removed and reinserted.
As per FIG. 1, a conventional driving machine includes an outer body frame 1 defining therein an internal accumulator chamber 2 where compressed air is accumulated. In the body frame 1 there are provided a cylinder 8 having a flange 8a, a piston 5 reciprocally movable in the cylinder 8, and a head valve 6 involved in returning the reciprocating piston 5 to its initial position to complete each stroke cycle. An ejector 3 is provided at an end of one stroke of the piston 5 and in which a fastener 4 such as a nail is positioned. Further, a trigger valve 7 is provided for opening and closing the head valve 6. An air chamber S is defined by a space below the flange 8a of the cylinder 8 and in between the body 1 and an outer peripheral surface of the cylinder 8 for returning the piston 5 to its initial position.
As shown in FIGS. 2 and 3, the body frame 1 is formed with an internal annular groove 1a. Further, a stop washer 9 rests on an upper surface of the flange 8a and is engaged with the annular groove 1a in order to prevent the cylinder 8 from moving axially upward. The stop washer 9 has inwardly bent end lip portions 9a extending radially inwardly for changing a diameter of the resultant washer 9 by pinching the lip portions 9a together.
The accumulator chamber 2 must be isolated from the air chamber S. To this effect, the flange 8a mates with a sealing area 1b of the body frame 1, and an O-ring 10 is installed in an annular groove 8d of the flange 8a. The stop washer 9 is made from a resilient material and is fitted to about one half its radial width into the groove 1a. The remaining portion of the stop washer 9, which radially inwardly projects from the groove 1a, rests on the upper surface of the flange 8a. (It should be noted that the upper surface of the flange 8a is in alignment with a lower wall of the annular groove 1a). By making use of radially outward self expansion force of the stop washer 9, the stop washer 9 can be held in the given position.
The inner peripheral surface portion of the body frame 1 is provided with a fixing region 1c at a position above the sealing area 1b. An inner diameter of the fixing region 1c is made equal to an inner diameter of the sealing area 1b so as to prevent upward movement of the stop washer 9, thus preventing upward movement of the cylinder 8.
When such conventional driving machine drives or ejects the fastener 4 into a workpiece, the opposite reaction to the action of the piston forces the cylinder 8 upwards in the direction opposite to the movement of the piston 5. Because the flange 8a is connected to the cylinder 8, the flange 8a also moves upward. Because the stop washer 9 rests on the upper surface of the flange 8a, the stop washer 9 is pushed upwards as the flange 8a rises. The stop washer 9 strikes against the fixing region 1c, deforming the same. This process occurs each time the drive machine is operated. Repeated operation may promote plastic deformation of the fixing region 1c to such extent that the inner diameter of the region 1c will be smaller than that of the sealing area 1b.
To disassemble the driving machine, particularly for removing the cylinder 8 from the body frame 1 for the purpose of maintenance or inspection, the stop washer 9 is first removed by pinching the lip ends 9a together, thus, decreasing the diameter of the stop washer 9. As a result, the stop washer 9 can be disengaged from the annular groove 1a. The cylinder 8 is therefore, freely movable upwardly for disassembly. If, however, the fixing region 1c is plastically deformed such that its inner peripheral portion bulges radially inwardly, and its inner diameter becomes smaller than that of the sealing area 1b, the O-ring 10 may abut the bulged portion, enter the groove 1a, and obstruct removal of the cylinder 8 from the body frame 1. If excessive force is applied to remove the cylinder, the O-ring 10 may be cut.